LIDAR signal acquisition

ABSTRACT

Methods and systems for combining return signals from multiple channels of a LIDAR measurement system are described herein. In one aspect, the outputs of multiple receive channels are electrically coupled before input to a single channel of an analog to digital converter. In another aspect, a DC offset voltage is provided at the output of each transimpedance amplifier of each receive channel to improve measured signal quality. In another aspect, a bias voltage supplied to each photodetector of each receive channel is adjusted based on measured temperature to save power and improve measurement consistency. In another aspect, a bias voltage supplied to each illumination source of each transmit channel is adjusted based on measured temperature. In another aspect, a multiplexer is employed to multiplex multiple sets of output signals of corresponding sets of receive channels before analog to digital conversion.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.application Ser. No. 16/134,000, filed on Sep. 18, 2018 and entitled“Lidar Signal Acquisition”, which, claims priority under 35 U.S.C. § 119from U.S. provisional patent application Ser. No. 62/559,783 entitled“LIDAR Signal Acquisition,” filed Sep. 18, 2017, the subject matter ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The described embodiments relate to LIDAR based 3-D point cloudmeasuring systems.

BACKGROUND INFORMATION

LIDAR systems employ pulses of light to measure distance to an objectbased on the time of flight (TOF) of each pulse of light. A pulse oflight emitted from a light source of a LIDAR system interacts with adistal object. A portion of the light reflects from the object andreturns to a detector of the LIDAR system. Based on the time elapsedbetween emission of the pulse of light and detection of the returnedpulse of light, a distance is estimated. In some examples, pulses oflight are generated by a laser emitter. The light pulses are focusedthrough a lens or lens assembly. The time it takes for a pulse of laserlight to return to a detector mounted near the emitter is measured. Adistance is derived from the time measurement with high accuracy.

Some LIDAR systems employ a single laser emitter/detector combinationcombined with a rotating mirror to effectively scan across a plane.Distance measurements performed by such a system are effectively twodimensional (i.e., planar), and the captured distance points arerendered as a 2-D (i.e. single plane) point cloud. In some examples,rotating mirrors are rotated at very fast speeds (e.g., thousands ofrevolutions per minute).

In many operational scenarios, a 3-D point cloud is required. A numberof schemes have been employed to interrogate the surrounding environmentin three dimensions. In some examples, a 2-D instrument is actuated upand down and/or back and forth, often on a gimbal. This is commonlyknown within the art as “winking” or “nodding” the sensor. Thus, asingle beam LIDAR unit can be employed to capture an entire 3-D array ofdistance points, albeit one point at a time. In a related example, aprism is employed to “divide” the laser pulse into multiple layers, eachhaving a slightly different vertical angle. This simulates the noddingeffect described above, but without actuation of the sensor itself.

In all the above examples, the light path of a single laseremitter/detector combination is somehow altered to achieve a broaderfield of view than a single sensor. The number of pixels such devicescan generate per unit time is inherently limited due limitations on thepulse repetition rate of a single laser. Any alteration of the beampath, whether it is by mirror, prism, or actuation of the device thatachieves a larger coverage area comes at a cost of decreased point clouddensity.

As noted above, 3-D point cloud systems exist in several configurations.However, in many applications it is necessary to see over a broad fieldof view in both horizontal and vertical directions. For example, in anautonomous vehicle application, the vertical field of view should extenddown as close as possible to see the ground in front of the vehicle. Inaddition, the vertical field of view should extend above the horizon, inthe event the car enters a dip in the road. In addition, it is necessaryto have a minimum of delay between the actions happening in the realworld and the imaging of those actions. In some examples, it isdesirable to provide a complete image update at least five times persecond. To address these requirements, a 3-D LIDAR system has beendeveloped that includes an array of multiple laser emitters anddetectors. This system is described in U.S. Pat. No. 7,969,558 issued onJun. 28, 2011, the subject matter of which is incorporated herein byreference in its entirety.

In many applications, a sequence of pulses is emitted. The direction ofeach pulse is sequentially varied in rapid succession. In theseexamples, a distance and intensity measurement associated with eachindividual pulse can be considered a pixel, and a collection of pulsesemitted and captured in rapid succession (i.e., “point cloud”) can berendered as an image or analyzed for other reasons (e.g., detectingobstacles). In some examples, viewing software is employed to render theresulting point clouds as images that appear three dimensional to auser. Different schemes can be used to depict the LIDAR measurements as3-D images that appear as if they were captured by a live action camera.

To measure a three dimensional environment with high resolution,throughput, and range, the measurement pulses must be very narrow andrepeat at high periodicity. Current systems suffer from low resolutionbecause they are limited in their ability to generate short durationpulses and resolve short duration return pulses at high frequency.

Saturation of the detector limits measurement capability as targetreflectivity and proximity vary greatly in realistic operatingenvironments. Power consumption may cause overheating of the LIDARsystem. Light devices, targets, circuits, and temperatures vary inactual systems. The variability of all of these elements limits systemperformance without proper calibration of each LIDAR channel.

Improvements in the drive electronics and receiver electronics of LIDARsystems are desired to improve imaging resolution and range.

SUMMARY

Methods and systems for combining return signals from multiple channelsof a LIDAR measurement system onto the input of a single channel of ananalog to digital converter are described herein.

In one aspect, the outputs of multiple receive channels of a LIDARmeasurement system are electrically coupled before input to a singlechannel of an analog to digital converter.

In a further aspect, the electrical elements in each electrical pathfrom each photodetector of multiple receive channels of a LIDARmeasurement system to an analog to digital converter are direct current(DC) coupled to one another.

In another aspect, a DC offset voltage is provided at the output of eachtransimpedance amplifier of each receive channel of a LIDAR measurementsystem to improve measured signal quality.

In another aspect, a bias voltage supplied to each photodetector of eachreceive channel of a LIDAR measurement system is adjusted based on ameasured temperature associated with elements of the receive channels tosave power and improve measurement consistency.

In another aspect, a bias voltage supplied to each illumination sourceof each transmit channel of a LIDAR measurement system is adjusted basedon a measured temperature associated with elements of the transmitchannels.

In another aspect, a multiplexer is disposed between multiple sets ofreceive channels and a single channel of an analog to digital converterto multiplex the output signals of the sets of receive channels beforeanalog to digital conversion to enhance measurement throughput.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of a multiple channel LIDAR measurementsystem 120 in one embodiment.

FIG. 2 depicts a set of N receive channels of multiple channel LIDARmeasurement system 120 in one embodiment.

FIG. 3 depicts a set of N transmit channels of multiple channel LIDARmeasurement system 120 in one embodiment.

FIG. 4 depicts two sets of multiple receive channels of a multiplechannel LIDAR measurement system in another embodiment.

FIG. 5 depicts an illustration of the timing associated with theemission of a measurement pulse from a measurement channel of LIDARmeasurement device 120 and capture of the returning measurement pulse.

FIG. 6 is a diagram illustrative of an embodiment of a 3-D LIDAR system100 in one exemplary operational scenario.

FIG. 7 is a diagram illustrative of another embodiment of a 3-D LIDARsystem 10 in one exemplary operational scenario.

FIG. 8 depicts a diagram illustrative of an exploded view of 3-D LIDARsystem 100 in one exemplary embodiment.

FIG. 9 depicts a view of optical elements 116 of 3-D LIDAR system 100 ingreater detail.

FIG. 10 depicts a cutaway view of optics 116 of 3-D LIDAR system 100 toillustrate the shaping of each beam of collected light 118.

FIG. 11 depicts a flowchart illustrative of a method 200 of performing aLIDAR measurement by a multiple channel LIDAR measurement system in atleast one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

Methods and systems for combining return signals from multiple channelsof a LIDAR measurement system onto the input of a single channel of ananalog to digital converter are described herein.

FIG. 1 depicts a multiple channel LIDAR measurement system 120 in oneembodiment. LIDAR measurement system 120 includes a master controller190 and N LIDAR measurement channels 125A-N, where N is any positive,integer number. Each channel of LIDAR measurement system 120 includes atransmit channel (e.g., transmit channels 160A-N) and a correspondingreceive channel (e.g., receive channels 130A-N).

As depicted in FIG. 1, each LIDAR transmit channel 160A-N includes anillumination source 163A-N. An illumination driver of each transmitchannel 160A-N causes each corresponding illumination source 163A-N toemit a measurement pulse of illumination light 164A-N in response to apulse trigger signal 151A-N received from corresponding receive channel130A-N. Each measurement pulse of illumination light 164A-N passesthrough mirror element 121A-N and illuminates a volume of thesurrounding environment. Each amount of return light 136A-N reflectedfrom object(s) at each illuminated location in the surroundingenvironment is incident on corresponding mirror elements 121A-N. Anovermold lens 131A-N is mounted over each photodetector 132A-N,respectively. Each overmold lens 131A-N includes a conical cavity thatcorresponds with the ray acceptance cone of return light 136A-N,respectively. Return light 136A-N is reflected from mirrors 121A-N tocorresponding photodetectors 132A-N, respectively.

As depicted in FIG. 1, illumination light 164A-N emitted from eachchannel of LIDAR measurement system 120 and corresponding returnmeasurement light 136A-N directed toward LIDAR measurement system 120share a common optical path.

As depicted in FIG. 1, each illumination source 163A-N is locatedoutside the field of view of each photodetector. Illumination light164A-N from illumination sources 163A-N is injected into thecorresponding detector reception cone through an opening in mirrors121A-N, respectively.

In some embodiments, each illumination source 163A-N is laser based(e.g., laser diode). In some embodiments, each illumination source isbased on one or more light emitting diodes. In general, any suitablepulsed illumination source may be contemplated.

Master controller 144 is configured to generate pulse command signals122A-N communicated to receive channels 130A-N, respectively. In theseembodiments, master controller 144 communicates a pulse command signalto each different LIDAR measurement channel. In this manner, mastercontroller 144 coordinates the timing of LIDAR measurements performed byany number of LIDAR measurement channels. Each pulse command signal is adigital signal generated by master controller 144. Thus, the timing ofeach pulse command signal is determined by a clock associated withmaster controller 144.

In some embodiments, each pulse command signal 122A-N is directly usedto trigger pulse generation by transmit channels 160A-N and dataacquisition by each corresponding receive channels 130A-N, respectively.However, transmit channels 160A-N and receive channels 130A-N do notshare the same clock as master controller 144. For this reason, preciseestimation of time of flight becomes much more computationally tediouswhen a pulse command signal is directly used to trigger pulse generationand data acquisition.

In some other embodiments, each receive channel 130A-N receives a pulsecommand signal 122A-N and generates corresponding pulse trigger signals151A-N, in response to pulse command signals 122A-N, respectively. Eachpulse trigger signal 151A-N is communicated to transmit channel 160A-Nand directly triggers an illumination driver associated with eachtransmit channel to generate a corresponding pulse of illumination light164A-N. In addition, each pulse trigger signal 151A-N directly triggersdata acquisition of return signals 136A-N and associated time of flightcalculations. In this manner, pulse trigger signals 151A-N generatedbased on the internal clock of return signal receivers of each receivechannel 130A-N, respectively, are employed to trigger both pulsegeneration and return pulse data acquisition for a particular LIDARmeasurement channel. This ensures precise synchronization of pulsegeneration and return pulse acquisition which enables precise time offlight calculations by time-to-digital conversion.

In one aspect, the outputs of each receive channel 130A-N areelectrically coupled (e.g., at voltage node 140). In this manner, theoutputs of receive channels 130A-N are effectively summed at the inputof the analog to digital converter 143.

FIG. 2 depicts a more detailed view of the receive channels of LIDARmeasurement system 120 in one embodiment. Like numbered elementsdescribed with respect to FIG. 1 are analogous to those illustrated inFIG. 2, and vice-versa. As depicted in FIG. 2, LIDAR measurement system120 includes a number of analog receive channels 130A-N, an analog todigital converter (ADC) 143, and a master controller 144.

As depicted in FIG. 2, each analog receive channel 130A-N includes aphotodetector (e.g., an avalanche photodiode 132A-N, or otherphotosensitive device) and a trans-impedance amplifier (TIA) 133A-N. Inaddition, each analog receive channel includes one or more secondaryamplifier stages 134A-N. However, in general, secondary amplifier stages134A-N are optional.

In the embodiment depicted in FIG. 2, incoming light 136A is detected byAPD 132A. In response to an incoming return pulse of light 136A, APD132A generates a current signal 137A. TIA 133A receives current signal137A and generates a voltage signal present at voltage node 138A. In theembodiment depicted in FIG. 2, TIA 133A generates a single ended voltageoutput. However, in some other embodiments, TIA 133A generates adifferential voltage output. Amplifier 134A amplifies the voltage signalat node 138A and generates an output signal 139A. In some embodimentsthe output of amplifier 134A is a current signal. However, in some otherembodiments, the output of amplifier 134A is a voltage signal. Asdepicted in FIG. 2, output signal 139A is the output of receive channel130A generated in response to detected return pulse of light 136A.Similarly, each receive channel 130A-N generates an output signal 139A-Nindicative of the detected return pulse of light 136A-N detected at eachreceive channel 130A-N, respectively.

As depicted in FIG. 2, the outputs of each receive channel 130A-N areelectrically coupled at voltage node 140. In this manner, the outputs ofreceive channels 130A-N are effectively summed. Combined output signal152 is an analog signal indicative of the output of each receive channel130A-N in the same sequence as the sequence of laser pulse emissionassociated with each receive channel 130A-N.

The summed signals are subsequently provided as input to a singlechannel of an analog to digital converter 143, either directly, or afterfurther processing (e.g., amplification by amplifier 142). In theembodiment depicted in FIG. 2, the summed output signal 152 is amplifiedby amplifier 142. Amplified signal 146 is converted to a digital signal147 by ADC 143. Digital signal 147 is received by master controller 144.

Alternatively, in the absence of amplifier 142, the outputs of receivechannels 130A-N are effectively summed at the input of ADC 143 (e.g., asdepicted in FIG. 1). In general, amplifier 142 is optional.

In a further aspect, the electrical elements in each electrical pathfrom a photodetector (e.g., APD 132A-N) to ADC 143 are direct current(DC) coupled to one another. In other words, for each receive channel130A-N, there are no explicitly formed energy storage elements that actas DC signal blocking elements (e.g., capacitors, etc.) between any ofAPD 132A-N, TIA 133A-N, amplifier 134A-N, amplifier 142, and ADC 143;only electrical conductors. In the embodiment depicted in FIG. 2, eachAPD 132A-N is DC coupled to a corresponding TIA 133A-N. Each TIA 133A-Nis DC coupled to a corresponding amplifier 134A-N. Each amplifier 134A-Nis DC coupled to amplifier 142. Amplifier 142 is DC coupled to ADC 143.

In another aspect, a DC offset voltage is provided at the output of theTIA associated with each receive channel.

In the embodiment depicted in FIG. 2, master controller 144 communicatesa command signal 145 to local controller 190. Command signal 145 isindicative of a desired DC voltage offset at the output of each TIA ofreceive channels 130A-N. Local controller 190, in turn, communicates DCoffset voltage signals 148A-N to voltage nodes 138A-N (via digital toanalog converter 191) at the outputs of TIA 133A-N, respectively. Insome embodiments, master controller 144 and local controller 190 areseparate devices. However, in some other embodiments, a single device isemployed to generate and communicate DC offset voltage signals to theoutput of each TIA. In some embodiments, master controller 144 is afield programmable gate array (FPGA) device and local controller 190 isa complex programmable logic device (CPLD). However, in general, anysuitable computing device may be employed.

In some embodiments, master controller 144 generates command signal 145based on the quality of measured signal 147. In some examples, commandsignal 145 is generated to maximize the signal to noise ratio of thedigital signals 147 generated by ADC 143. In some examples, commandsignal 145 is generated to offset DC noise signals present in theoperating environment of the LIDAR device. By offsetting DC noise, thefull scale of ADC 143 is available for dynamic measurement. Thisincreases signal to noise ratio.

In another aspect, the temperature associated with one or more receivechannels is measured. In a further aspect, the measured temperature isemployed to adjust a bias voltage supplied to each APD.

In the embodiment depicted in FIG. 2, a temperature sensor module islocated in close proximity to one or more elements of receive channels130A-N (i.e., elements of a receive subsystem including receive channels130A-N). In one example, temperature sensor module 150 is located within40 millimeters of a receive channel (e.g., any of receive channels130A-N). However, in general, a temperature sensor may be located at anysuitable distance from one or more receive channels. Temperature sensormodule 150 measures temperature where module 150 is located andcommunicates a digital signal 151 indicative of the measured temperatureto master controller 144 (e.g., over a serial peripheral interface). Inresponse to the measured temperature, master controller communicates acommand signal 176 to local controller 190. Command signal 176 isindicative of a desired bias voltage provided to each APD of receivechannels 130A-N. Local controller 190, in turn, communicates biasvoltage command signals 177A-N to APD bias power supplies 131A-D,respectively (via digital to analog converter 191). Each APD bias powersupply 131A-N adjusts a bias voltage signal 135A-N provided to each APD132A-N, respectively.

In some embodiments, master controller 144 and local controller 190 areseparate devices. However, in some other embodiments, a single device isemployed to generate and communicate bias voltage signals to each APDbias power supply.

Master controller 144 generates command signal 176 based on the measuredtemperature associated with one or more receive channels. Command signal176 is generated to save power and improve measurement consistency.

In another aspect, the temperature associated with one or more transmitchannels is measured. In a further aspect, the measured temperature isemployed to adjust a bias voltage supplied to each illumination source.

FIG. 3 depicts a more detailed view of the transmit channels of LIDARmeasurement system 120 in one embodiment. Like numbered elementsdescribed with respect to FIG. 1 are analogous to those illustrated inFIG. 3, and vice-versa. FIG. 3 depicts a set of N transmit channels160A-N (where N can be any positive integer number). Each transmitchannel includes a power supply 161A-N and an illumination source 163A-N(e.g., a laser diode). Each illumination source 163A-N emits a pulse oflight 164A-N. Light reflected from the surrounding environment isdetected by a corresponding receiver channel (e.g., receiver channels130A-N depicted in FIG. 2). The time of flight associated each pulse oflight determines the distance between the LIDAR device and the detectedobject in the surrounding environment.

As depicted in FIG. 3, a temperature sensor module 165 is located inclose proximity to one or more elements of transmit channels 160A-N(i.e., elements of a transmit subsystem including transmit channels160A-N). In one example, temperature sensor module 165 is located within40 millimeters of a transmit channel 160A-N. However, in general, atemperature sensor may be located at any suitable distance from one ormore transmit channels. Temperature sensor module 165 measurestemperature where module 165 is located and communicates a digitalsignal 166 indicative of the measured temperature to master controller144 (e.g., over a serial peripheral interface). In response to themeasured temperature, master controller 144 communicates a commandsignal 167 to local controller 168. Command signal 167 is indicative ofa desired bias voltage provided to each laser diode of transmit channels160A-N. Local controller 168, in turn, communicates bias voltage commandsignals 149A-N to power supply 161A-D, respectively (via digital toanalog converter 169). Each power supply 161A-N adjusts a bias voltagesignal 162A-N provided to each laser diode 163A-N, respectively.

In some embodiments, master controller 144 and local controller 168 areseparate devices. However, in some other embodiments, a single device isemployed to generate and communicate bias voltage signals to each biaspower supply.

In some embodiments, master controller 144 generates command signal 167based on the measured temperature associated with one or more transmitchannels and also the level of signal detected at each correspondingreceive channel (e.g., signals 139A-N).

In a further aspect, a multiplexer is disposed between multiple sets ofreceive channels and ADC 143 to enhance measurement throughput.

FIG. 4 depicts two sets of multiple receive channels of a multiplechannel LIDAR measurement system in another embodiment. Like numberedelements described with respect to FIG. 1 are analogous to thoseillustrated in FIG. 4, and vice-versa. FIG. 4 depicts receive channels130A-N and an additional set of receive channels 170A-N. The outputs ofreceive channels 130A-N are electrically coupled at voltage node 140 asdescribed hereinbefore. Similarly, the outputs of receive channels170A-N are electrically coupled at voltage node 171. In the embodimentdepicted in FIG. 4, a two channel multiplexer 141 receives the summedoutput signals 140 and 171 and generates multiplexed output 145.Multiplexed output 145 is amplified by amplifier 142. Amplified signal146 is converted to a digital signal 147 by a single channel of ADC 143.Digital signal 147 is received by master controller 144. In this manner,the outputs of 2N receive channels are combined onto a single ADCchannel.

In one embodiment, each receive channel is fabricated onto a singleprinted circuit board. A group of N boards are electrically coupled toanother printed circuit board that includes multiplexer 141, amplifier142, local controller 190, DAC 191, and temperature sensor module 150.ADC 143 and master controller 144 are assembled on yet another printedcircuit board. Similarly, each transmit channel is fabricated onto asingle printed circuit board. A group of N boards are electricallycoupled to another printed circuit board that includes temperaturesensor module 165, local controller 168, and DAC 169.

In some embodiments, illumination drivers, illumination sources 163A-N,photodetectors 132A-N, and return signal receivers are mounted, eitherdirectly or indirectly, to a common substrate (e.g., printed circuitboard) that provides mechanical support and electrical connectivityamong the elements.

In general, any of the power supplies described herein may be mounted toa separate substrate and electrically coupled to the various electronicelements in any suitable manner. Alternatively, any of the powersupplies described herein may be integrated with other electronicelements in any suitable manner.

The power supplies described herein may be configured to supplyelectrical power specified as voltage or current. Hence, any electricalpower source described herein as a voltage source or a current sourcemay be contemplated as an equivalent current source or voltage source,respectively.

FIG. 5 depicts an illustration of the timing associated with theemission of a measurement pulse from an LIDAR measurement device andcapture of the returning measurement pulse. As depicted in FIG. 5, ameasurement is initiated by the rising edge of pulse trigger signal 122Agenerated, for example, by master controller 144. A measurement window(i.e., a period of time over which collected return signal data isassociated with a particular measurement pulse) is initiated by enablingdata acquisition at the rising edge of pulse trigger signal 122A. Theduration of the measurement window, T_(measurement), corresponds to thewindow of time when a return signal is expected in response to theemission of a measurement pulse sequence. In some examples, themeasurement window is enabled at the rising edge of pulse trigger signal122A and is disabled at a time corresponding to the time of flight oflight over a distance that is approximately twice the range of the LIDARsystem. In this manner, the measurement window is open to collect returnlight from objects adjacent to the LIDAR system (i.e., negligible timeof flight) to objects that are located at the maximum range of the LIDARsystem. In this manner, all other light that cannot possibly contributeto useful return signal is rejected.

As depicted in FIG. 5, return signal 147 includes three returnmeasurement pulses 147A-C that correspond with the emitted measurementpulse. Any of these instances may be reported as potentially validdistance measurements by the LIDAR system.

In another aspect, a master controller is configured to generate aplurality of pulse command signals, each communicated to different LIDARmeasurement channels.

FIGS. 6-8 depict 3-D LIDAR systems that include multiple LIDARmeasurement channels. In some embodiments, a delay time is set betweenthe firing of each LIDAR measurement channel. In some examples, thedelay time is greater than the time of flight of the measurement pulsesequence to and from an object located at the maximum range of the LIDARdevice. In this manner, there is no cross-talk among any of the LIDARmeasurement channels. In some other examples, a measurement pulse isemitted from one LIDAR measurement channel before a measurement pulseemitted from another LIDAR measurement channel has had time to return tothe LIDAR device. In these embodiments, care is taken to ensure thatthere is sufficient spatial separation between the areas of thesurrounding environment interrogated by each beam to avoid cross-talk.

FIG. 6 is a diagram illustrative of an embodiment of a 3-D LIDAR system100 in one exemplary operational scenario. 3-D LIDAR system 100 includesa lower housing 101 and an upper housing 102 that includes a domed shellelement 103 constructed from a material that is transparent to infraredlight (e.g., light having a wavelength within the spectral range of 700to 1,700 nanometers). In one example, domed shell element 103 istransparent to light having a wavelengths centered at 905 nanometers.

As depicted in FIG. 6, a plurality of beams of light 105 are emittedfrom 3-D LIDAR system 100 through domed shell element 103 over anangular range, α, measured from a central axis 104. In the embodimentdepicted in FIG. 5, each beam of light is projected onto a plane definedby the x and y axes at a plurality of different locations spaced apartfrom one another. For example, beam 106 is projected onto the xy planeat location 107.

In the embodiment depicted in FIG. 6, 3-D LIDAR system 100 is configuredto scan each of the plurality of beams of light 105 about central axis104. Each beam of light projected onto the xy plane traces a circularpattern centered about the intersection point of the central axis 104and the xy plane. For example, over time, beam 106 projected onto the xyplane traces out a circular trajectory 108 centered about central axis104.

FIG. 7 is a diagram illustrative of another embodiment of a 3-D LIDARsystem 10 in one exemplary operational scenario. 3-D LIDAR system 10includes a lower housing 11 and an upper housing 12 that includes acylindrical shell element 13 constructed from a material that istransparent to infrared light (e.g., light having a wavelength withinthe spectral range of 700 to 1,700 nanometers). In one example,cylindrical shell element 13 is transparent to light having awavelengths centered at 905 nanometers.

As depicted in FIG. 8, a plurality of beams of light 15 are emitted from3-D LIDAR system 10 through cylindrical shell element 13 over an angularrange, β. In the embodiment depicted in FIG. 8, the chief ray of eachbeam of light is illustrated. Each beam of light is projected outwardinto the surrounding environment in a plurality of different directions.For example, beam 16 is projected onto location 17 in the surroundingenvironment. In some embodiments, each beam of light emitted from system10 diverges slightly. In one example, a beam of light emitted fromsystem 10 illuminates a spot size of 20 centimeters in diameter at adistance of 100 meters from system 10. In this manner, each beam ofillumination light is a cone of illumination light emitted from system10.

In the embodiment depicted in FIG. 7, 3-D LIDAR system 10 is configuredto scan each of the plurality of beams of light 15 about central axis14. For purposes of illustration, beams of light 15 are illustrated inone angular orientation relative to a non-rotating coordinate frame of3-D LIDAR system 10 and beams of light 15′ are illustrated in anotherangular orientation relative to the non-rotating coordinate frame. Asthe beams of light 15 rotate about central axis 14, each beam of lightprojected into the surrounding environment (e.g., each cone ofillumination light associated with each beam) illuminates a volume ofthe environment corresponding the cone shaped illumination beam as it isswept around central axis 14.

FIG. 8 depicts an exploded view of 3-D LIDAR system 100 in one exemplaryembodiment. 3-D LIDAR system 100 further includes a lightemission/collection engine 112 that rotates about central axis 104. Asdepicted in FIG. 8, a central optical axis 117 of lightemission/collection engine 112 is tilted at an angle, θ, with respect tocentral axis 104. 3-D LIDAR system 100 includes a stationary electronicsboard 110 mounted in a fixed position with respect to lower housing 101.Rotating electronics board 111 is disposed above stationary electronicsboard 110 and is configured to rotate with respect to stationaryelectronics board 110 at a predetermined rotational velocity (e.g., morethan 200 revolutions per minute). Electrical power and electronicsignals are communicated between stationary electronics board 110 androtating electronics board 111 over one or more transformer elements,capacitive elements, or optical elements, resulting in a contactlesstransmission of these signals. Light emission/collection engine 112 isfixedly positioned with respect to the rotating electronics board 111,and thus rotates about central axis 104 at the predetermined angularvelocity, ω.

As depicted in FIG. 8, light emission/collection engine 112 includes anarray of printed circuit boards 114, each including a transmit channel(e.g., transmit channels 160A-N). Light emitted from the illuminationsource associated with each of the transmit channels is directed towarda mirror (not shown). Light reflected from the mirror passes through aseries of illumination optics 115 that collimate the emitted light intothe array of beams of light 105 that are emitted from 3-D LIDAR system100 as depicted in FIG. 6. In general, any number of light emittingelements can be arranged to simultaneously, or substantiallysimultaneously, emit any number of light beams from 3-D LIDAR system100. In addition, any number of light emitting elements can be arrangedto sequentially emit any number of light beams from 3-D LIDAR system100. In one embodiment, two or more light emitting elements aretriggered to emit light substantially simultaneously, and then after aprogrammed period of time has elapsed, another two or more lightemitting elements are triggered to emit light substantiallysimultaneously. Light reflected from objects in the environment iscollected by collection optics 116. Collected light associated with eachillumination beam passes through collection optics 116 where it isfocused onto each respective detecting element of an array of printedcircuit boards 113, each including a receive channel (e.g., receivechannels 130A-N). After passing through collection optics 116, thecollected light is reflected from a mirror (not shown) onto eachdetector element. In practice, crosstalk among each measurement channellimits the number of channels that can be triggered simultaneously.However, to maximize imaging resolution, it is desirable to trigger asmany channels as possible, simultaneously, so that time of flightmeasurements are obtained from many channels at the same time, ratherthan sequentially.

FIG. 9 depicts a view of optical elements 116 in greater detail. Asdepicted in FIG. 9, optical elements 116 include four lens elements116A-D arranged to focus collected light 118 onto each detector of thearray of receive channels 113. In the embodiment depicted in FIG. 9,light passing through optics 116 is reflected from mirror 124 and isdirected onto each detector of the array of receive channels 113. Insome embodiments, one or more of the optical elements 116 is constructedfrom one or more materials that absorb light outside of a predeterminedwavelength range. The predetermined wavelength range includes thewavelengths of light emitted by the array of receive channels 113. Inone example, one or more of the lens elements are constructed from aplastic material that includes a colorant additive to absorb lighthaving wavelengths less than infrared light generated by each of thearray of receive channels 113. In one example, the colorant is Epolight7276A available from Aako BV (The Netherlands). In general, any numberof different colorants can be added to any of the plastic lens elementsof optics 116 to filter out undesired spectra.

FIG. 10 depicts a cutaway view of optics 116 to illustrate the shapingof each beam of collected light 118.

In this manner, a LIDAR system, such as 3-D LIDAR system 10 depicted inFIG. 7, and system 100, depicted in FIG. 6, includes a plurality ofLIDAR measurement channels each emitting a pulsed beam of illuminationlight from the LIDAR device into the surrounding environment andmeasuring return light reflected from objects in the surroundingenvironment.

In some embodiments, such as the embodiments described with reference toFIG. 6 and FIG. 7, an array of LIDAR measurement channels is mounted toa rotating frame of the LIDAR device. This rotating frame rotates withrespect to a base frame of the LIDAR device. However, in general, anarray of LIDAR measurement channels may be movable in any suitablemanner (e.g., gimbal, pan/tilt, etc.) or fixed with respect to a baseframe of the LIDAR device.

In some other embodiments, each LIDAR measurement channel includes abeam directing element (e.g., a scanning mirror, MEMS mirror etc.) thatscans the illumination beam generated by the LIDAR measurement channel.

In some other embodiments, two or more LIDAR measurement channels eachemit a beam of illumination light toward a scanning mirror device (e.g.,MEMS mirror) that reflects the beams into the surrounding environment indifferent directions.

In a further aspect, one or more LIDAR measurement channels are inoptical communication with an optical phase modulation device thatdirects the illumination beam(s) generated by the one or more LIDARmeasurement channels in different directions. The optical phasemodulation device is an active device that receives a control signalthat causes the optical phase modulation device to change state and thuschange the direction of light diffracted from the optical phasemodulation device. In this manner, the illumination beam(s) generated bythe one or more integrated LIDAR devices are scanned through a number ofdifferent orientations and effectively interrogate the surrounding 3-Denvironment under measurement. The diffracted beams projected into thesurrounding environment interact with objects in the environment. Eachrespective LIDAR measurement channel measures the distance between theLIDAR measurement system and the detected object based on return lightcollected from the object. The optical phase modulation device isdisposed in the optical path between the LIDAR measurement channel andan object under measurement in the surrounding environment. Thus, bothillumination light and corresponding return light pass through theoptical phase modulation device.

FIG. 11 illustrates a flowchart of a method 200 suitable forimplementation by multiple channel LIDAR measurement system as describedherein. In some embodiments, multiple channel LIDAR measurement system120 is operable in accordance with method 100 illustrated in FIG. 11.However, in general, the execution of method 200 is not limited to theembodiments of multiple channel LIDAR measurement system 120 describedwith reference to FIG. 1. These illustrations and correspondingexplanation are provided by way of example as many other embodiments andoperational examples may be contemplated.

In block 201, a measurement pulse of illumination light is emitted fromeach of a first plurality of LIDAR measurement channels.

In block 202, an amount of return light reflected from a point in athree dimensional environment in response to each measurement pulse ofillumination light is detected.

In block 203, a return signal indicative of each amount of return lightis generated.

In block 204, an indication of each return signal is provided to a firstshared output node of the first plurality of LIDAR measurement channels.

In block 205, an indication of each return signal of the first pluralityof LIDAR measurement channels is received at an input channel of ananalog to digital converter.

A computing system as described herein may include, but is not limitedto, a personal computer system, mainframe computer system, workstation,image computer, parallel processor, or any other device known in theart. In general, the term “computing system” may be broadly defined toencompass any device having one or more processors, which executeinstructions from a memory medium.

Program instructions implementing methods such as those described hereinmay be transmitted over a transmission medium such as a wire, cable, orwireless transmission link. Program instructions are stored in acomputer readable medium. Exemplary computer-readable media includeread-only memory, a random access memory, a magnetic or optical disk, ora magnetic tape.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

What is claimed is:
 1. A LIDAR measurement system, comprising: a firstplurality of LIDAR measurement channels each comprising: an illuminationsource operable to emit a measurement pulse of illumination light; aphotodetector configured to detect an amount of return light reflectedfrom a surface in an environment in response to the measurement pulse ofillumination light; and a return signal receiver configured to generatea return signal indicative of the detected amount of return light and toprovide the return signal to a first shared output node of the firstplurality of LIDAR measurement channels, wherein the return signalreceiver includes a respective amplifier; an analog to digital converterhaving an input channel, wherein the analog to digital converter isconfigured to receive each return signal of the first plurality of LIDARmeasurement channels provided to the first shared output node at theinput channel of the analog to digital converter; and a controllerconfigured to provide a direct current (DC) voltage offset signal to theamplifier of the return signal receiver of each of the first pluralityof LIDAR measurement channels and to generate a command signal to adjusta bias voltage supplied to one or more of the illumination sources ofone or more of the first plurality of LIDAR measurement channels basedon a transmit subsystem temperature.
 2. The LIDAR measurement system ofclaim 1, further comprising: a second plurality of LIDAR measurementchannels each comprising: an illumination source operable to emit ameasurement pulse of illumination light; a photodetector configured todetect an amount of return light reflected from a surface in theenvironment in response to the measurement pulse of illumination light;and a return signal receiver configured to generate a return signalindicative of the detected amount of return light and to provide thereturn signal to a second shared output node of the second plurality ofLIDAR measurement channels; and an analog multiplexer having a firstinput channel coupled to the first shared output node, a second inputchannel coupled to the second shared output node, and an output channelcoupled to the input channel of the analog to digital converter.
 3. TheLIDAR measurement system of claim 1, the first plurality of LIDARmeasurement channels each further comprising: an illumination bias powersupply coupled to the one or more illumination sources, wherein theillumination bias power supply is configured to adjust the bias voltagesupplied to the one or more illumination sources in response to thecommand signal.
 4. The LIDAR measurement system of claim 3, furthercomprising a temperature sensor disposed in close proximity to at leastone of the illumination sources of the first plurality of LIDARmeasurement channels, wherein the controller is electrically coupled tothe temperature sensor and the illumination bias power supply, whereinthe controller is configured to receive an indication of the transmitsubsystem temperature measured from the temperature sensor, wherein thecommand signal indicates a desired bias voltage, and wherein thecontroller is configured to generate the command signal based at leastin part on the measured transmit subsystem temperature.
 5. The LIDARmeasurement system of claim 3, wherein the controller is electricallycoupled to the analog to digital converter and the illumination biaspower supply associated with the one or more illumination scores,wherein the controller is configured to receive an indication of eachreturn signal of the one or more LIDAR measurement channels and generatethe command signal indicative of the desired bias voltage based at leastin part on the respective return signals corresponding with each of theone or more LIDAR measurement channels.
 6. The LIDAR measurement systemof claim 1, the first plurality of LIDAR measurement channels eachfurther comprising: a photodetector bias power supply coupled to thephotodetector, wherein the photodetector bias power supply is configuredto provide a desired amount of electrical bias power to thephotodetector in response to a command signal.
 7. The LIDAR measurementsystem of claim 6, further comprising a temperature sensor disposed inclose proximity to one or more of the return signal receivers andphotodetectors of the first plurality of LIDAR measurement channels,wherein the controller is electrically coupled to the temperature sensorand each photodetector bias power supply associated with each of thefirst plurality of LIDAR measurement channels, wherein the controller isconfigured to receive an indication of a receive subsystem temperaturemeasured from the temperature sensor and communicate the command signalindicative of the desired amount of electrical bias associated with eachof the first plurality of LIDAR measurement channels based on themeasured receive subsystem temperature.
 8. The LIDAR measurement systemof claim 1, wherein the amplifier of the return signal receiver of eachof the first plurality of LIDAR measurement channels has an input nodeand an output node, wherein the input node is coupled to an output ofthe photodetector of the respective LIDAR measurement channel.
 9. TheLIDAR measurement system of claim 8, wherein the controller iselectrically coupled to the output node of the amplifier of the returnsignal receiver of each of the first plurality of LIDAR measurementchannels, wherein the controller is configured to provide the DC offsetvoltage at the output node of each of the amplifiers.
 10. The LIDARmeasurement system of claim 9, wherein the LIDAR measurement system isconfigured to provide the DC offset voltage at the output nodes of theamplifiers to increase signal to noise ratios of corresponding digitalsignals generated by the analog to digital converter.
 11. A LIDARmeasurement system, comprising: a first plurality of LIDAR receivechannels each comprising: a photodetector configured to detect an amountof return light reflected from a surface in an environment in responseto a measurement pulse of illumination light from an illustrationsource; and an amplifier coupled to the photodetector, the amplifierconfigured to generate a signal indicative of the return light; ananalog to digital converter having an input channel configured toreceive the signals indicative of the return light associated with eachof the first plurality of LIDAR receive channels, the signals providedto a first shared output node of the first plurality of LIDAR receivechannels; and a controller configured to provide a direct current (DC)voltage offset signal to the amplifier of each of the LIDAR receivechannels and to generate a command signal to adjust a bias voltagesupplied to one or more of the illumination sources of one or more ofthe first plurality of LIDAR measurement channels based on a transmitsubsystem temperature.
 12. The LIDAR measurement system of claim 11,wherein the controller is electrically coupled to an output node of eachof the amplifiers of the first plurality of LIDAR measurement channels,wherein the controller is configured to provide the DC offset voltage atthe output node of each of the amplifiers.
 13. The LIDAR measurementsystem of claim 12, wherein the DC offset voltage is provided at theoutput node of each of the amplifiers to increase signal to noise ratiosof corresponding digital signals generated by the analog to digitalconverter.
 14. A method comprising: with each of a first plurality ofLIDAR measurement channels: emitting, from an illumination source, ameasurement pulse of illumination light; detecting an amount of returnlight reflected from a respective surface in an environment in responseto the measurement pulse of illumination light; generating, with areturn signal receiver including an amplifier, a return signalindicative of the amount of return light; providing, by the returnsignal receiver, the return signal to a first shared output node of thefirst plurality of LIDAR measurement channels; and receiving each returnsignal of the first plurality of LIDAR measurement channels at an inputchannel of an analog to digital converter; providing a direct current(DC) offset voltage to the amplifier of the return signal receiver ofeach of the first plurality of LIDAR measurement channels; and adjustinga bias voltage supplied to one or more of the illumination sources ofone or more of the first plurality of LIDAR measurement channels basedon a transmit subsystem temperature.
 15. The method of claim 14, furthercomprising: with each of a second plurality of LIDAR measurementchannels: emitting a measurement pulse of illumination light; detectingan amount of return light reflected from a respective surface in theenvironment in response to the measurement pulse of illumination light;generating, with a return signal receiver including an amplifier, areturn signal indicative of each amount of return light; and providing,by the return signal receiver, the return signal to a second sharedoutput node of the second plurality of LIDAR measurement channels;generating a multiplexed output signal indicative of the return signalsof the first plurality of LIDAR measurement channels and the returnsignals of the second plurality of LIDAR measurement channels; andreceiving the multiplexed output signal at the input channel of theanalog to digital converter.
 16. The method of claim 14, furthercomprising: measuring a temperature of a location in close proximity toat least one of the illumination sources of the first plurality of LIDARmeasurement channels, wherein the transmit subsystem temperature is themeasured temperature.
 17. The method of claim 14, further comprising:receiving respective indications of return signals of the one or moreLIDAR measurement channels, wherein the adjusting of the bias voltagesupplied to the one or more illumination sources is also based on therespective indications of the return signals.
 18. The method of claim14, further comprising: measuring a temperature of a location proximateto one or more photodetectors and one or more return signal receivers ofthe first plurality of LIDAR measurement channels; and adjusting anamount of electrical bias power provided to each of the one or morephotodetectors based at least in part on the measured temperature. 19.The method of claim 14, wherein the DC offset voltage is generated toincrease signal to noise ratios of corresponding digital signalsgenerated by the analog to digital converter.
 20. The method of claim 2,wherein the analog multiplexer is configured to receive the returnsignals of the first plurality of LIDAR measurement channels provided tothe first shared output node at the first input channel, receive thereturn signals of the second plurality of LIDAR measurement channelsprovided to the second shared output node at the second input channel,and generate a multiplexed output signal indicative of the returnsignals of the first plurality and second plurality of LIDAR measurementchannels at the output channel.